<div class="alert alert-danger" *ngIf="!items.length">
  没有相关主题
</div>
<div class="list-group padding-h-neg" *ngIf="items.length">
  <a class="list-group-item" *ngFor="let item of items" [routerLink]="['../', item.id]">
    {{item.title}}
  </a>
</div>
